Methods and compositions for the treatment of plant growth media

ABSTRACT

Crop yields are significantly enhanced by treating soil or other plant growing media with a fungicidally or pesticidally effective amount of metham, the fungicidally or pesticidally effective amount being insufficient to significantly retard growth of a plant. In the practice of the invention, the soil or growing media surrounding roots of growing plants is treated with metham by dripping an aqueous solution of metham onto the media, by injecting the aqueous solution into the soil, by irrigating the soil or by drenching or spraying the soil with the aqueous solution. Significantly reduced amounts of metham are employed to reduce damage to the plant or vegetative material.

RELATED APPLICATIONS

This is a continuation-in-part of U.S. application Ser. No. 412,883,filed Sept. 26, 1989, now U.S. Pat. No. 4,994,487.

FIELD OF THE INVENTION

This invention relates to methods and compositions for the fungicidaland/or pesticidal treatment of soil and other plant growth media withmetham sodium to enhance plant development and growth.

BACKGROUND OF THE INVENTION

Metham sodium (sodium methyldithiocarbamate, also knows as methamsodium, metham and metham, and marketed under the names Metam, SectagonII, Soil-Prep, Vapam and V.P.M.) is commercially available for use as apreplanting soil fumigant solution for plant crops. After application tothe soil, the liquid solution is converted into a gaseous fumigant,methyl isothiocyanate, which is known to be effective as a fungicide,pesticide and herbicide for the control of weeds, germinating weed seedsand insects, such as Henbit, Lambsquarters, Pigweed, Careless weed,Watergrass, Johnsongrass, Nutgrass, Wild morning-glory, Purslane,Nematodes, Symphylids, and as a pesticide/fungicide for the control ofsoil-borne diseases, such as Rhizoctonia, Phythium, Phytophora,Vericillium, Sclerotinia, Oat root fungus and Club root of crucifers. Ina 32.7% aqueous solution (3.18 pounds by dry weight of active ingredientper gallon), metham sodium is conventionally applied as a preplantingfumigant at application rates of 50-100 gallons (159-318 pounds by dryweight of active ingredient) per acre.

Due to its highly toxic nature, planting may not take place until 14-21days after conventional metham sodium application for well-drained soilsof light-to-medium texture, for 30 days after conventional treatment forsoils that are heavy or especially high in organic matter (or thatremain wet and/or cold), or until at least 60 days after conventionaltreatment where metham sodium dosages greater than 100 gallons per acrehave been applied.

The fumigant and/or fungicidal activity of metham sodium andbiologically active derivatives and analogs of metham sodium have beenknown in the art for some time. For example, U.S. Pat. No. 2,614,957discloses a fungicidal composition containing about 75 to about 99% byweight of a metham sodium analog, sodium dimethyldithiocarbamate, andabout 25 to about 1% by weight of the sodium salt of2-mercaptobenzothiozol.

U.S. Pat. Nos. 2,614,959 and 2,776,922 disclose the fungicidal activityof compositions of the zinc salt of dimethyldithiocarbamate combinedwith the ferric or zinc salt of mercaptobenzothiozol.

U.S. Pat. No. 2,792,327 discloses a method of controlling fungusinfestation by applying sodium monomethyl dithiocarbamate directly tothe locus of the vegetation to be treated for fungus control. Inpractice, metham sodium is applied in a foliar application to plantleaves or as a preplant seed treatment. It is stated that the method canbe used to treat living plants, such as crop plants, ornamental plants,fruit bearing trees, and plant seeds. Suitable application rates arestated to be about 1 to 4 pounds per acre for use as a foliar spray,about 0.5-3 oz. per 100 pounds of seed to be treated, or about 0.005 to0.02 pounds of sodium monomethyl dithiocarbamate per pound of organicmatter treated.

U.S. Pat. No. 2,835,625 discloses a fungicidal metham sodium derivative,isopropoxycarbonyl dimethyldithiocarbamate.

U.S. Pat. No. 3,699,231 discloses the use of a mixture of metham sodiumand formaldehyde in a 1/1 weight ratio to inhibit the growth ofbacteria, such as in drilling fluids.

In addition, metham sodium has been used in the art in connection withthe preservation of harvested crops. For example, U.S. Pat. No.3,836,655 discloses a composition of metham sodium and propionic acidfor use in preserving moist grain during storage. U.S. Pat. No.4,708,879 discloses the use of metham sodium for preserving highmoisture forage crops, such as hay, to prevent microbial degradationduring storage.

The use of metham sodium as a preplanting herbicide applied throughsprinkler systems, low-volume drip irrigation systems, subsurfaceblading and as a drench, is described in detail in Fischer et al., "TheUse of Metham For Weed Control--A Progress Report," Runcina, Vol. 41,University of California Cooperative Extension, Fresno County, pp. 1-17(1989). Its use as a herbicide, fungicide and nematocide has continuedessentially unchanged for at least the last 30 years. While the soilfumigant and fungicidal properties of metham sodium are well known inthe art, its highly toxic nature presents difficulties when used inconnection with crop planting for fungicidal purposes. For example, asconventionally applied, a significant amount of time ranging from about7 days to about 60 days must elapse prior to crop planting in order toprevent metham sodium damage to the newly planted crop. This results notonly in significant time delays between fungicide application and cropplanting, but also requires multiple pass working of the crop field. Inaddition, the relatively high cost of metham sodium makes conventionalapplication prohibitively expensive for marginal application conditions.

SUMMARY OF THE INVENTION

It has now been discovered that the foregoing problems can be overcomeand that crop yields can be significantly enhanced by treating soil orother plant growth media in which plants are growing with a fungicidallyor pesticidally effective amount of metham, the fungicidally effectiveamount being insufficient to significantly retard growth of the plantsin the soil or plant growth media. In the practice of the invention,soil or growth medium in which plants are growing is treated with methamby drenching the soil or growth media with an aqueous solution of methamin the vicinity of established plant crops. As compared to conventionalmetham application methods, significantly reduced amounts of metham areemployed to reduce damage to the growing plant. It has surprisingly beenfound that metham retains sufficient fungicidal and pesticidal activitywhen employed in the practice of the present invention to favorablyalter the soil biology to significantly enhance crop yields.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, soil or other plant growthmedium surrounding established plant crops is treated by contacting thesoil with a fungicidally or pesticidally effective amount of metham, theamount being insufficient to significantly reduce or retard plantgrowth. Since the amounts of metham used to treat growing media inaccordance with the invention are substantially less than thoseconventionally used to obtain herbicidal, fungicidal and nematocidalactivity, a significant advantage of the invention is the ability to beable to treat media in which desired plants are growing, as opposed to10-60 days prior to planting using conventional techniques.

Metham, when formulated in aqueous solution at about 3.0-3.5 pounds ofactive ingredient per gallon, is a nonvolatile material. However, uponcontact with soil, metham chemically decomposes to produce methylisothiocyanate, a volatile, highly toxic gas. Decomposition of metham tomethyl isothiocyanate typically occurs within about 5 hours of treatmentof the soil. Thereafter, the methyl isothiocyanate further decomposes inthe soil to nontoxic compounds.

As such herein, the term "metham" includes methyldithiocarbamate and itsfungicidally effective salts. In a presently particularly preferredembodiment, metham is used in the form of sodium N-methyldithiocarbamate dihydrate (metham sodium), although it is to beunderstood that other analogues or salts of N-methyldithiocarbamate,such as potassium N-methylidithiocarbamate are included in the termmetham and may be employed in the practice of the invention.

As used herein, the term "growing medium", "growing media" or "growthmedia" includes, but is not limited to, soil, peat moss, sand, pumice,organic mulches and other media which support plant life.

In one presently preferred embodiment, growing media in which desiredplant materials are growing is treated by contacting the growing mediawith a dilute aqueous solution of metham, such as, for example, bydripping, spraying, injecting, irrigating or drenching the growing mediain the vicinity of growing plant roots. Accordingly, established plantcrops may be advantageously affected by treatment of the growth mediumsurrounding the plant crops. The practice of the invention is broadlyapplicable to a variety of plants and growing vegetative material,including, for example, grasses, dry beans, dry peas, soy beans, sweetcorn, field corn, green beans, green peas, cotton, wheat, barley,lentils, potatoes, pineapple, flower bulbs, container grown ornamentals,fruit trees, vegetable seedlings, turf grass and the like.

The precise amount of metham to be applied to a particular plant crop inaccordance with the invention will depend upon the sensitivities of theparticular crop, the method of application, the depth of the media to betreated and other field or greenhous conditions. Generally, however,metham is applied in the form of an aqueous solution in amountsequivalent to about 15 ppm to about 2,000 ppm, more preferably fromabout 30 ppm to about 1,000 ppm, of a 32.7% aqueous solution of methamfor those applications where the soil is drenched or vegetative materialis directly contacted with the aqueous solution. In a presentlypreferred, illustrative embodiment wherein an aqueous solution of methamis employed in irrigation water, as a drench or as a spray which resultsin contact of plant foliage with the aqueous solution, the plant foliageis optionally but preferably washed with at least about 0.01 inch ofwater, more preferably with at least about 0.10 inch of water, aftermetham treatment to remove substantially all of the metham from theplant foliage.

These and other embodiments in the invention may be better understood inconnection with the following representative examples, which arepresented for purposes of illustration of the invention and not by wayof limitation.

EXAMPLE 1 Drip Application in Seed Furrow

The effect of application of metham in the seed furrow at time ofseeding of the crop was determined in the following manner. A diluteaqueous solution of metham was prepared by mixing one part of metham(VAPAM, Stauffer Chemical Company, Westport, Conn., U.S.A., 3.18pounds/gallon of active material) with nine parts of water. A seed bedwas prepared in Skagit County, Washington, U.S.A., and planted in rowswith 1 meter spacing with seed of field corn, green peas, green beansand dry peas. Test sections for each crop consisted of a single 6 meterrow, with 4 replicates for each metham treatment level for each crop. Atthe time of planting of the seed, the dilute aqueous metham was meteredinto the seed row through a 1/4 inch (inside diameter) polyethylene tubetipped with a flexible rubber tube that was set in the planter to dragon the bottom of the seed furrow. The rates of application were variedto determine the effect on crop yields, and are listed in Table I asweight of metham (active ingredient) per unit length of row treated. Thecrops were allowed to grow for the number of days indicated in Table 1,and then 2 meter sections from each replicate were harvested and weighedfor total green weight. The results are shown in Table 1 as the averageyield (green weight) per meter of row.

                  TABLE 1                                                         ______________________________________                                        Rate of Application                                                                        Average yield in grams/meter of row                              grams/ Ounces/   Field    Green  Green  Dry                                   meter  1000 ft   corn     peas   beans  peas                                  ______________________________________                                        0      0          820     350    306    252                                   0.0312 0.335     1003     383    400    340                                   0.0624 0.671     1093     473    383    340                                   0.1249 1.344     1030     287    240    525                                   0.2499 2.688      700     100     73    315                                   0.4998 5.375      590      23     0      67                                   Growth period (days)                                                                        34       39       33     27                                     ______________________________________                                    

EXAMPLE 2

The effect of varying rates of metham application for the control ofseeding diseases of peas was determined as follows. A greenhouse growingmedium (Rediearth plus vermiculite 50:50, mix) was inoculated with 2 gof disease-infested field soil (known to contain Fusarium, Pythium, andAphanomyces) per 100 cc of medium, and one crop of peas was grown in themedium to increase the natural disease level of the original field soil.The inoculated medium was then placed in 15.24 cm plastic pots and a30.48 cm row (seed furrow) was marked in each pot. Green pea seeds,Puget variety, were planted in the medium in the seed furrow (10 seedsper pot), metham was applied in an aqueous solution to the seed furrowin an amount equivalent to 1.64 ml per meter of row, and then the seedfurrow was immediately covered with 2.5 cm of the disease-infestedgrowing medium. Varying concentrations of metham were employed, as shownin Table 2, with rates of application listed as dry weight of metham perunit length of row treated. Each pot was a single replication with 5replicates being made at each treatment level. After 39 days, the plantsin each pot were harvested by cutting at ground level and the plantyield (green weight) for each replicate (pot) was determined. Theresults are shown in the following Table 2.

                  TABLE 2                                                         ______________________________________                                                     Average Yield (grams)                                            Rate of Application                                                                          Average*                                                       Grams/   Ounces/   emergence                                                  meter row                                                                              1000 ft   seedlings Per Pot Per Plant                                ______________________________________                                        0        0         8.2       6.9     0.83                                     0.00312  0.0335    8.7       8.6     0.98                                     0.00624  0.0671    8.7       7.9     0.90                                     0.01249  0.1344    8.7       8.5     0.97                                     0.02499  0.2688    9.5       10.0    1.05                                     0.06248  0.671     9.7       9.5     1.00                                     0.12496  1.344     9.0       9.1     0.93                                     ______________________________________                                         *Average seedling emergence based on 10 seeds planted                    

EXAMPLE 3 Injection Application Below Seed Furrow

The effect of applying metham by injection below the seed furrow at timeof seeding of the crop was determined by injecting an aqueous solutionof metham 20 cm below the soil surface in a field seed bed in SkagitCounty, Washington, U.S.A., using rigid shanks (5/8 by 11/2 by 24inches) equipped with a small diamond shaped point. At the time of soilinjection of the aqueous solution, pea seeds were planted in a seedfurrow having a depth of 2.5 cm below the soil surface and locateddirectly over the metham injection line. The rates of metham applicationwere varied to determine the effect on plant yield, and are listed inTable 3 as weight of metham (active ingredient) per unit length of rowtreated. Each replicate consisted of a single row 6 meters in length,with 4 replications being made at each metham treatment level and rowsbeing spaced 1 meter apart. After 92 days, 2 meter sections from eachreplicate were harvested and weighed for total green weight. The resultsare shown in Table 3 as the average yield (green weight) per plant.

                  TABLE 3                                                         ______________________________________                                        Average green weight in grams/plant harvested                                 from two meters of row.                                                       Application Rate        Yield (grams)                                         Grams/    Ounces/       Plant   Pod                                           meter     1000 ft       weight  weight                                        ______________________________________                                        0         0             147     78                                             0.0624*   0.671*        220*   113*                                          0.0624    0.671         219     112                                           0.1249    1.344         211     95                                            0.1874    1.874         172     86                                            ______________________________________                                         *Application of aqueous solution of metham in the seed furrow at time of      planting, a comparison to injection                                      

EXAMPLE 4 Spray Application to Soil Around Vegetative Material

The effect of applying metham as a spray to soil surrounding a newlyplanted reproductive vegetative plant part was determined as follows. Anaqueous solution was prepared containing 2286 ppm of metham by dryweight of active ingredient (or 6,000 ppm of a 32.7% aqueous methamformulation). A greenhouse growing medium (Rediearth plus vermiculite50:50 mix) was placed in 15.2 cm plastic pots, one pot for eachreplicate. A furrow was prepared in each pot for receiving a potato seedpiece. The aqueous solution of metham was sprayed into the furrow,followed by planting of a potato seed piece in the furrow and then asecond application of the aqueous metham solution over the planted seedpiece. The rate of metham applied in this manner was varied by applyingvarying total amounts of liquid, with rates of application listed inTable 4 as weight of metham (by dry weight of active ingredient) perunit area or length of row treated. Four replicates were made at eachtreatment level. After planting, the potatoes were grown in a greenhousefor 34 days and then harvested. The average green weight (above groundparts) and tuber weight was determined as shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Application Rate                                                                             Equivalent Rate                                                Grams/  Ounces/    (gallons/acre)***                                                                           Weight (grams)                               sq. meter*                                                                            1000 ft row**                                                                            6,000 ppm 32.7% Vines Tubers                               ______________________________________                                        0       0          0         0     88.7  72.7                                 0.503   0.824      13.1      0.079 96.5  85.5                                 1.007   1.650      26.2      0.158 104.7 78.2                                 2.015   3.022      53.4      0.316 92.5  71.7                                 3.022   4.951      79.6      0.474 47.9  52.0                                 ______________________________________                                          *dry weight of metham per square meter                                        **rate in ounces of 32.7% aqueous metham solution per 1,000 feet of          planted row, treating a 6 cm band                                             ***based on a 42 inch row spacing and a 6 cm treatment band in each row  

EXAMPLE 5 Post-Planting Drench Application

The effect of applying metham as a post-plant drench for the control ofpests in a vegetative reproductive structure was determined by plantingiris bulbs in 15.2 cm pots containing a greenhouse growing medium(perlite, vermiculite and peat moss). Immediately after planting,approximately 1.3 cm (0.51 inches) of an aqueous solution metham wasapplied to each pot. The concentration of metham in the aqueous solutionwas varied from 304 to 2438 ppm of metham by dry weight (or 800 to 6,400ppm of a 32.7% aqueous metham formulation). Four replicates at eachtreatment level were made. The iris plants were grown in a greenhouse inSkagit County, Washington, U.S.A., for 66 days, harvested, and analyzedfor average green weight and presence of nematodes, as shown in Table 5.The nematode value is given as the average number of Ditylenchusdestructor recovered from one gram of bulb tissue.

                  TABLE 5                                                         ______________________________________                                        Application Rate     Top                                                      g/meter.sup.2 *                                                                         ppm**      weight (g)                                                                              Nematodes***                                   ______________________________________                                        0            0       25.8      848                                            3.952       800      25.1      798                                            7.917     1,600      23.6      158                                            15.847    3,200      24.4       64                                            31.694    6,400      23.8       24                                            ______________________________________                                          *based on application of 1.3 cm of aqueous solution                           **ppm of 32.7% aqueous metham solution                                       ***number of nematodes recovered from 1 g of bulb tissue 66 days after        treatment                                                                

EXAMPLE 6 Drench To Soil Surrounding Living Plants

Metham was applied as a drench in approximately 2.5 cm of water atconcentrations ranging from 0 to 1,000 ppm of aqueous metham as a drenchon soil containing established grass (turf type) in a 10 cm plastic pot.The grass foliage was then lightly syringed with water to remove excessmetham from the grass foliage. Each treatment was replicated 5 times.The grass was grown in a greenhouse and then harvested by clipping to auniform height over a period of about 7 weeks. The data are presented inTable 6 as the average green weight of grass clippings harvested fromeach treatment by date. Rates of application are listed as weight andppm of metham per unit of area treated.

                                      TABLE 6                                     __________________________________________________________________________    Rate of Application*                                                          g/  Pounds/Acre                                                                          ml/        Weight at harvest by date (g)                           meter.sup.2                                                                       equivalent**                                                                         meter.sup.2 ***                                                                     ppm****                                                                            12/6                                                                              12/20                                                                             1/25                                                                             Total                                        __________________________________________________________________________    0   0      0      0    9  13  2  24                                           0.952                                                                             8.51   2.5   100  13  23  2  38                                           1.905                                                                             10.03  5     200  46  150 9  204                                          3.810                                                                             34.07  10    400  27  22  7  56                                           5.715                                                                             51.11  15    600  11  36  4  51                                           7.620                                                                             68.15  20    800  25  16  10 51                                           9.529                                                                             85.23  25    1,000                                                                              30  63  26 119                                          __________________________________________________________________________      *Rates of application calculated on application of 2.5 cm of water per       square meter or acre of land.                                                  **dry weight of metham per square meter                                       ***ml of a 32.7% aqueous metham solution per square meter                    ****ppm of a 32.7% formulation, aqueous metham solution                  

EXAMPLE 7 Phytotoxicity to Living Plants

The phytotoxicity of metham to Cotoneaster when applied as a drench toplants growing in one gallon containers was determined by applyingaqueous solutions containing varying amounts of metham to soil in thecontainers in which healthy Cotoneaster plants were growing. The ratesof application were varied as listed in Table 7 in ppm of a 32.7% methamaqueous solution and applied in 250 ml of liquid per container, allowingfor some of the aqueous metham solution to leach from the containers.After 72 days, the plant foliage was analyzed, as shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Application                                                                   Rate         Phytotoxicity rating                                             (ppm metham) rep 1       rep 2  rep 3                                         ______________________________________                                        0            1           1      1                                             57.1         1           1      1                                             114.3        1           2      1                                             228.6        1           2      2                                             342.9        3           2      2                                             ______________________________________                                         Toxicity readings:                                                            1 = normal growth                                                             2 = slight foliage discoloration                                              3 = marked foliage discoloration                                              4 = death of part of all of plant                                        

Greenhouse assay of metham treated soil and laboratory assay of soil hasindicated kill of most of the soil-borne plant pathogens at levels of 50to 350 ppm of metham by dry weight of active ingredient in aqueoussolution.

EXAMPLE 8 Phytotoxicity to Established Turf Grass

The phytotoxicity of metham to established turf grass in the field whenapplied as a drench was determined by applying aqueous solutionscontaining varying amounts of metham to turf grass in either 2.5 or 5 cmof water. The rates of application were varied from 0 to 1968 ppm of a32.7% aqueous solution of metham, as listed in Table 8. After 21 days,the plant foliage was analyzed, as shown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Application    Phytotoxicity rating                                           Rate           Amount of Solution (cm)                                        (ppm metham)   2.5 cm     5 cm                                                ______________________________________                                         0             1          1                                                   328            1          2                                                   656            1          3                                                   1312           2          4                                                   1968           4          5                                                   ______________________________________                                         Toxicity readings:                                                            1 = normal growth                                                             2 = slight foliage discoloration                                              3 = moderate foliage discoloration                                            4 = severe foliage discoloration                                              5 = death of part or all of aerial plant parts                           

After 42 days, the grass in all treated areas appeared normal. Nopermanent kill of the turf was observed at the rates of metham solutionsused in this experiment.

EXAMPLE 9 Toxicity to Nematodes

The differential toxicity of aqueous solutions of metham on nematodesand growth of plants was tested as follows.

Soil collected from two fields naturally infested with nematodes(placing the soil on free-living and cyst, Heterodera spp.) was treatedby non-gauze milk filters supported in trays with a screen bottom.Radish seeds were added to the soil and allowed to germinate and emerge.The trays containing soil and emerged radish plants were suspended overcontainers containing 250 ml of an aqueous solution of metham inconcentrations ranging from 0 to 350 ppm of 32.7% formulated metham. Thetrays were suspended in a manner to allow the soil in the tray to becomesaturated with the aqueous solution but not to a depth which wouldsubmerge the soil in the metham solution. After 4 days, trays wereremoved and the emerged radish seedlings counted. The aqueous methamsolution in the containers under the soil trays was concentrated to 2 mland the nematodes identified and counted. The data in Table 9 are asummary of the results of this test. Free-living nematodes are listed asactive and inactive. The inactive nematodes were active for sufficienttime to penetrate the filter pad and be collected in the container.However, examination of the inactive forms of nematodes established thatthe nematodes were killed by the metham solution.

                  TABLE 9                                                         ______________________________________                                        Radish Seedling Growth and Nematode Recovery                                  Application                                                                   Rate*      Radish      Nematodes***                                           (ppm metham)                                                                             Emergence** Total    Active Cyst                                   ______________________________________                                        Soil 1:                                                                        0         ++           90      85     0                                       75        ++          120       3     0                                      150        ++          120       0     0                                      250        ++           80       0     2                                      350        ++           90       0     0                                      Soil 2:                                                                        0         ++          270      255    30                                      75        ++          730      11     1                                      150        ++          490       1     0                                      250        ++          320       0     0                                      350        ++          240       1     0                                      ______________________________________                                          *Concentration of metham in ppm of formulated 32.7% active ingredient         **Radish emergence: ++ indicates normal growth of radish seedlings           ***Nematode counts: Total and active nematodes recovered from 15 ml of        soil                                                                     

While the invention has been described in connection with certainillustrative and presently preferred embodiments, various modificationswill be apparent to those skilled in the art. Any such modifications areintended to be within the scope of the appended claims, except insofaras precluded by the prior art.

What is claimed is:
 1. A method of enhancing plant growth, comprisingtreating growing medium in which plants are growing with a fungicidallyor pesticidally effective amount of metham, said fungicidally orpesticidally effective amount being insufficient to significantly retardgrowth of the plants.
 2. The method of claim 1 wherein the medium istreated with metham by applying an aqueous solution to the medium bydripping, spraying, injecting or drenching the solution onto the medium.3. The method of claim 2 wherein the aqueous solution is applied at rateequivalent to about 30 to about 1000 ppm of a 32.7% aqueous solution ofmetham.
 4. The method of claim 1, wherein the metham is applied inirrigation water as a drench or as a spray, and which further compriseswashing the foliage of the plants with at least about 0.01 inch of waterafter metham treatment to remove substantially all of the metham fromthe foliage.